Nadal and Muguruza win ITF player of the year awards2017 AP YEAR END PHOTOS - Rafael Nadal, of Spain, reacts after beating Kevin Anderson, of South Africa, to win the men's singles final of the U.S. Open tennis tournament on Sept. 10, 2017, in New York. (AP Photo/Seth Wenig)
At 31, Nadal becomes the oldest ITF men's world champion after a season in which he won a 10th French Open and a third U.S. Open.
The Spaniard also became the oldest player to finish the year at No. 1 since the ATP rankings began in 1973.
Muguruza dropped only one set en route to her first Wimbledon title and finished the year at No. 2 behind Simona Halep.
''Becoming ITF world champion in such a competitive year is amazing for me,'' said Muguruza, who is also Spanish. ''(Nadal) is a great role model for all of us, so it is a great moment for tennis in Spain.''